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Tectonic and Stratigraphic Setting of Gas Fields of the North Coast Marine Area, Offshore Northern Trinidad and Tobago Basin

Punnette, Stefan 1; Mann, Paul 1; Escalona, Alejandro 2
1 The University of Texas at Austin, Austin, TX.
2 Department of Petroleum Engineering, University of Stavanger, Stavanger, Norway.

The North Coast Marine Area 1 (NCMA1) exploration block is a 500 km2 exploration block that is located 40 km north of the island of Trinidad and 60 km west of the island of Tobago. The block straddles the east-northeast-trending continental shelf of northern offshore Trinidad and slope of the 14 km- -deep Tobago basin. Gas was discovered in 1971 and wells drilled at shelfal depths commenced development on two (Hibiscus, Chaconia) of three large gas fields in 2001. All gas production is presently restricted to the NCMA shelf edge although present exploration for gas and condensate is being carried out along the deeper water slope of the Tobago basin. In this presentation we show a series of academic, deep penetration 2D lines to illustrate: 1) the deep and shallow structure of the Hinge Line fault zone (HLFZ), the main structure underlying the NCMA1 production area and responsible for structural traps within the field that is producing from Pliocene reservoirs. The HLFZ is a down-to-the-northwest fault with apparent normal throw; 2) the presence of the Middle Miocene unconformity beneath the NCMA1 and onto the Trinidad shelf; this unconformity is locally angular and may act as a structural trap; 3) the correlation of Paleogene and Neogene units present in the adjacent 14 km-thick Tobago basin and thinning across the shelf-slope break and onto the northern Trinidad shelf; the deep Tobago basin is filled by two megasequences (1 and 2) of Paleogene to Middle Miocene age and totaling 11.5 km in thickness; and 4) possible gas and condensate updip migration routes from a zone of potential mature source rocks at depths of 8 to 11 km beneath the Tobago basin. Thermal modeling shows that Paleogene rocks are mature at depths of 5.4 to 9 km in the Tobago basin and may have generated thermogenic gas; updip migration of gas from these depths indicates that faults of the HLFZ at the basin edge are non-sealing and allow the migration of basin-derived gas into shallow reservoirs beneath the shelf area.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009